Comparison of volumetric loss and surface roughness of composite dental restorations obtained by additive and subtractive manufacturing methods

Statement of problem

Permanent crown materials produced with new generation additive manufacturing and traditional subtractive manufacturing materials have not been compared in terms of wear resistance.

Purpose

This study aims to compare the volumetric loss related to wear and resulting surface roughness after aging in a chewing simulator between resin nano ceramics produced with milling technique and permanent crown materials produced with three dimensional (3D) printing.

Materials and methods

Three different hybrid composite-ceramic (HCC) (The three materials are GC: Cerasmart, VE: Vita Enamic, and GV: Grandio Voco.) and one 3D printed definitive crown resin (FormLabs Permanent Crown Resin) were investigated before aging (n:8), the surface roughness of all samples was measured with a profilometer, and 1 randomly selected sample from each subgroup was imaged with scanning electron microscope (SEM). 3D scans of each sample were obtained with a desktop scanner. Thermomechanical aging was performed using a chewing simulator. Four hundred thousand cycles were completed under a vertical occlusal force of 49 ± 0.7 N with a thermal cycle of 1.7 Hz 5-55° and with a dwell time of 120 s, mimicking 2 years of aging. The imaging procedures were repeated, and the change in surface roughness was evaluated. 3D images were also overlapped, and the volumetric loss was calculated with the relevant inspector software. The data obtained were analyzed by two-way ANOVA (p < 0.05).

Result

The results showed significant statistical differences for both parameters (p > 0.05). The highest volumetric loss was found in the GV group while the lowest volumetric loss was in the VE group. The highest surface roughness values were observed in the GV group, while the lowest values belonged to the VE one.

Conclusion

Of the restorative materials evaluated, the VE group is suitable for long-term restorations, whereas the GV one is suitable for medium-term restorations. It is promising in terms of 3D printing technologies that the 3D material gives comparable results with the GV group.

Clinical i̇mplication

Additive manufacturing techniques are a successful method that accelerates the manufacturing process. Permanent crown resins are promising alternatives to conventional production.

Etching Patterns of Self-Etching Primers in Relation to Shear Bond Strength on Unground Enamel Samples

It was the intention of the study to evaluate the etching effects of several self-etching primers on unground enamel and their relevance for shear bond strength testing. Seven self-etching primers (Clearfil SE, Futurabond NR, M-Bond, One Coat, Optibond, Transbond SEP+, Xeno III) and a conventional 35% phosphoric gel acid were applied to bovine incisors according to the manufacturer's instructions. All specimens were analyzed by electron microscopy. A visual four-step grading was used for the characterization of the macroscopic (5000×) and microscopic (20,000×) etching patterns. In addition, shear bond strength for all the products was tested with an Instron 3344 after 1000 thermocycles between 5 °C and 55 °C. Statistical analysis was carried out using Kruskal-Wallis with Dunn's post-test and Pearson's correlation coefficient. Very strong etching patterns with well-defined prisms were found for the conventional etching, Transbond SEP+, and to a lesser degree, for Xeno III. Clearfil SE and Futurabond NR revealed moderate etching patterns, and M-Bond, One Coat, and Optibond revealed very weak etching patterns. The bond strength correlated well with the etching patterns. The highest shear strength was obtained with conventional etching and Transbond SEP+, followed by Clearfil SE. Moderate shear bond strengths were found for Xeno III, Futurabond NR, One Coat, and M-Bond, and the lowest were found with Optibond.

Effect of Polishing Systems on the Surface Roughness of Nano-Hybrid and Nano-Filling Composite Resins: A Systematic Review

Background: The polishing of surface roughness is an important characteristic of composite resins and is directly related to the longevity of the restoration and patient comfort. Different polishing systems utilize different protocols, as reported in the literature. This systematic review (SR) aimed to synthesize and analyze the available scientific evidence about the effect of polishing systems on the surface roughness of nano-hybrid and nano-filling composite resins. Methods: The study protocol of this SR was registered at the International Prospective Register of Systematic Reviews -PROSPERO- (CRD4201705653). A search was conducted in PubMed-Medline, Scopus, LILACS, EMBASE, for the period 2007–2020. Quality appraisal and a descriptive analysis of the papers that met the inclusion criteria were conducted. Results: 18 records were included. Seven polishing systems (PS) of one step were found, seven PS of two steps, eight PS of three steps, three PS of four steps, and four PS of five steps. Polishing protocols (PP) varied, with application times ranging from 10 s to 60 s with speeds between 10,000 and 30,000 RPM. Regarding composition, the aluminum oxide was one of the most important components used to achieve a smooth surface. Conclusions: Multistep polishing systems were the most effective (i.e., Astropol and Sof-Lex Discs).

Relationships between Flexural and Bonding Properties, Marginal Adaptation, and Polymerization Shrinkage in Flowable Composite Restorations for Dental Application

To evaluate the flexural and bonding properties, marginal adaptation, and polymerization shrinkage in flowable composite restorations and their relationships, four new generation flowable composites, one conventional, and one bulk-fill flowable composite were used in this study. Flexural properties of the composites and shear bond strength to enamel and dentin for flowable restorations were measured immediately and 24 h after polymerization. Marginal adaptation, polymerization shrinkage, and stress were also investigated immediately after polymerization. The flexural properties, and bond strength of the flowable composites to enamel and dentin were much lower immediately after polymerization than at 24 h, regardless of the type of the composite. Polymerization shrinkage and stress varied depending on the material, and bulk-fill flowable composite showed much lower values than the others. The marginal adaptation and polymerization shrinkage of the composites appeared to have a much stronger correlation with a shear bond strength to dentin than to enamel. The weak mechanical properties and bond strengths of flowable composites in the early stage after polymerization must be taken into account when using them in the clinic. In addition, clinicians should be aware that polymerization shrinkage of flowable composites can still lead to the formation of gaps and failure of adaptation to the cavity regardless of the type of composite.

Bonding and wear properties of self-adhesive flowable restorative materials

The purpose of this study was to evaluate the bonding and wear properties of self-adhesive flowable restorative materials. Five self-adhesive flowable restorative materials were used. The study parameters were: (i) shear bond strengths; (ii) microleakage; (iii) occlusal wear; and (iv) qualitative evaluation of the bonding interface. The range of shear bond strengths of the materials was as follows: 7.4-12.2 MPa to ground enamel, 22.5-32.5 MPa to etched enamel, and 1.3-4.2 MPa to dentin. The microleakage scores of the materials did not show any statistically significant differences regardless of the presence or absence of etching. The wear facets on the materials showed 0.099-0.447 mm³ of volume loss and 148.6-365.3 µm maximum depth, with statistically significant differences between materials. Scanning electron microscopic images of the interfaces of the materials showed good adaptation regardless of substrate. The bonding and wear properties of self-adhesive flowable restorative materials were still limited and showed lower values than previously reported results for nanofilled composites with an adhesive system. Selective enamel etching can improve the bonding performance of these materials.

Flexural properties and wear behavior of computer-aided design/computer-aided manufacturing resin blocks

This study investigates the flexural properties, Knoop hardness number (KHN), and wear behavior of computer-aided design and computer-aided manufacturing (CAD/CAM) resin blocks and compares these values with those of conventional resin composites for direct restoration (RCDs). Four CAD/CAM resin blocks and two RCDs are compared. Ten specimens per material are used to obtain the flexural properties according to ISO 6872 specifications, and five specimens per material are used for KHN measurement. For sliding impact wear testing, twelve specimens are prepared. Confocal laser scanning microscopy (LSM) is used to determine maximum facet depth and volume loss. Polished material surfaces and worn surfaces after wear testing are observed using scanning electron microscopy and LSM. While measured flexural properties and KHN are found to be material-dependent, CAD/CAM resin blocks exhibit higher wear resistance than RCDs. CAD/CAM resin blocks polymerized at high-pressure and high-temperature are found to exhibit wear behaviors far superior to those of RCDs.

Influence of Filler Loading on the Mechanical Properties of Flowable Resin Composites

The aim of this study was to evaluate the correlation between the percent of inorganic filler by weight (wt. %) and by volume (vol. %) of 11 flowable resin composites (FRCs) and their mechanical properties. To establish the correlation, the quantity of inorganic filler was determined by combustion and shape/size analyzed by SEM images. The compressive strength (CS), flexural strength (FS), and flexural modulus (FM) were determined. The CS values were between 182.87-310.38 MPa, the FS values ranged between 59.59 and 96.95 MPa, and the FM values were between 2.34 and 6.23 GPa. The percentage of inorganic filler registered values situated between 52.25 and 69.64 wt. % and 35.35 and 53.50 vol. %. There was a very good correlation between CS, FS, and FM vs. the inorganic filler by wt. % and vol. %. (R² = 0.8899–0.9483). The highest regression was obtained for the FM values vs. vol. %. SEM images of the tested FRCs showed hybrid inorganic filler for Filtek Supreme XT (A3) and StarFlow (A2) and a homogeneous type of inorganic filler for the other investigated materials. All of the FS values were above 50 MPa, the ISO 4049/2019 limit for FRCs.

Wear resistance of indirect composite resins used for provisional restorations supported by implants

PURPOSE

The aim of this study was to investigate simulated localized and generalized wear of indirect composite resins used for implant supported provisional restorations.

MATERIALS AND METHODS

The study investigated ten indirect composite resins. Two kinds of wear were simulated by 400,000 cycles in a Leinfelder-Suzuki (Alabama) machine. Localized wear was simulated with a stainless-steel ball bearing antagonist and generalized with a flat-ended stainless-steel cylinder antagonist. The tests were carried out in water slurry of polymethyl methacrylate beads. Wear was measured using a Proscan 2100 noncontact profilometer in conjunction with Proscan and AnSur 3D software.

RESULTS

Both localized and generalized wear were significantly different (P<.05) among the indirect composite resins. SR Nexco and Gradia Plus showed significantly less wear than the other indirect composite resins. The rank order of wear was same in both types of wear simulation.

CONCLUSION

Indirect composite resins are recommended when a provisional implant-supported restoration is required to function in place over a long period. Although only some indirect composite resins showed similar wear resistance to CAD/CAM composite resins, the wear resistance of all the indirect composite resins was higher than that of bis-acryl base provisional and polymethyl methacrylate resins.

Effectiveness of a universal adhesive for repair bonding to composite and amalgam

The study aimed to compare the repair bond strength of aged composite and amalgam repaired with resin composite after various mechanical and adhesive surface treatments. Specimens were aged by thermal cycling (10,000 cycles, 5-55°C) and randomly subjected to one of three surface treatments: diamond bur abrasion, aluminum oxide air abrasion, or silica coating. Conventional bonding or a universal adhesive with incorporated silane was applied afterward (each n = 16) and resin composite was attached. In the control groups (each n = 16), resin composite was attached using one of the above adhesives without prior mechanical surface conditioning. After further thermal cycling, the shear bond strength (SBS) and failure modes were assessed. Statistical analyses were performed using ANOVA, Weibull statistics, two sample t-tests, and Chi²-test (P < 0.05). The SBS of the repaired amalgam was significantly lower than that of the composite and mechanical pretreatment significantly increased SBS. The universal adhesive significantly improved the SBS of the repaired amalgam compared to the conventional bonding agent and mechanical pretreatment increased the number of cohesive/mixed failures. Amalgam restorations may be repaired using resin composites, but the resulting SBS is lower than that obtained with composite.

Bonding Interaction and Shrinkage Stress of Low-viscosity Bulk Fill Resin Composites With High-viscosity Bulk Fill or Conventional Resin Composites

OBJECTIVE

To analyze the shrinkage stress, bonding interaction, and failure modes between different low-viscosity bulk fill resin composites and conventional resin composites produced by the same manufacturer or a high-viscosity bulk fill resin composite used to restore the occlusal layer in posterior teeth.

METHODS & MATERIALS

Three low-viscosity bulk fill resin composites were associated with the conventional resin composites made by the same manufacturers or with a high-viscosity bulk fill resin composite, resulting in six groups (n=10). The bonding interaction between resin composites was tested by assessing the microshear bond strength (μSBS). The samples were thermocycled and were tested with 1-mm/min crosshead speed, and the failure mode was evaluated. The post-gel shrinkage (Shr) of all the resin composites was measured using a strain gauge (n=10). The modulus of elasticity (E) and the hardness (KHN) were measured using the Knoop hardness test. Two-dimensional finite element models were created for analyzing the stress caused by shrinkage and contact loading. The μSBS, Shr, E, and KHN data were analyzed using the Student t-test and one-way analysis of variance. The failure mode data were subjected to chi-square analysis (α=0.05). The stress distribution was analyzed qualitatively.

RESULTS

No significant difference was verified for μSBS between low-viscosity bulk fill resin composites and conventional or high-viscosity bulk fill composites in terms of restoring the occlusal layer (p=0.349). Cohesive failure of the low-viscosity bulk fill resin composites was the most frequent failure mode. The Shr, E, and KHN varied between low-viscosity and high-viscosity resin composites. The use of high-viscosity bulk fill resin composites on the occlusal layer reduced the stress at the enamel interface on the occlusal surface.

CONCLUSIONS

The use of high-viscosity bulk fill resin composites as an occlusal layer for low-viscosity bulk fill resin composites to restore the posterior teeth can be a viable alternative, as it shows a similar bonding interaction to conventional resin composites as well as lower shrinkage stress at the enamel margin.